Emission source having carbon nanotube, electron microscope using this emission source, and electron beam drawing device

ABSTRACT

The invention provides a high reliability emission source able to secure the ohmic contact of a carbon nanotube and an electrically conductive base material, and having sufficient joining strength and easily making a beam shaft adjustment. The invention also provides an electron microscope for realizing high resolution, high brightness, a reduction in sample damage due to a reduction in acceleration voltage, a reduction in cost and compactness, and an electron beam drawing device for realizing high definition, high efficiency, a reduction in cost and compactness in comparison with the conventional device kind by using this high reliability emission source. Therefore, in the emission source, the carbon nanotube is attached to the tip central portion of the electrically conductive base material through an electrically conductive joining material or an organic material. Thereafter, the carbon nanotube is joined to the electrically conductive base material in ohmic contact by carbonization-processing the organic material by heat treatment, or diffusive joining. This emission source is applied to the electron microscope and the electron beam drawing device.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an emission source having a carbon nanotube, an electron microscope and an electron beam drawing device using this emission source. Description of the Related Art The following four conditions are required to further raise resolution and brightness of the electron microscope. (1) The size of the emission source is reduced. (2) The brightness of the emission source is increased. (3) Electron energy width from the emission source is reduced to reduce the influence of chromatic aberration. (4) An emitted electron beam is stabilized. There are a thermal electron emission type constructed by LaB₆ as the emission source, a Schottky type constructed by ZrO/W, and a field emission type constructed by tungsten in which the tip of a needle is sharpened by electric field polishing. In view of high resolution and high brightness, the emission source of the field emission type is most excellent, but has the following defects. (1) Since no field emission is generated unless a super high vacuum state of 10⁻⁸ Pa or more is set, an exhaust system is large-sized so that it is difficult to make the device compact, and cost is increased. (2) Since no field emission is generated unless a drawing-out voltage is set to a high value such as several kV, an organic material and an organism relating sample promising for rapidly growing in the future are greatly damaged, and no sufficient high accuracy observation can be made. (3) An emission electric current is greatly changed in time by an emitter tip shape change due to the influence of a residual gas molecule adsorbed and desorbed on the emitter surface and the impact of a residual gas ion.

[0003] In a length measuring SEM (CDSEM) used in a semiconductor process, etc., a Schottky type emission source is used at present. However, higher resolution under a low acceleration voltage has become an important subject to prevent electric charging on the observation sample and reduce the damage of the sample.

[0004] Further, in an electron beam drawing device for irradiating the electron beam to a sample substrate coated with a resist sensitive to the electron beam and forming various kinds of circuit patterns, an emission source for obtaining a micro probe diameter is required as the various kinds of circuit patterns are highly defined. Thermal electron emission type sources constructed by tungsten and LaB₆ are conventionally used. However, these emission sources have advantages in that the beam electric current can be set to be large, but astigmatism caused by the size of an absolute emitter tip radius is large so that no drawing of 20 nm or less can be performed. Therefore, the field emission type source is recently used. However, a new problem exists in that the beam electric current is unstable by smallness of the beam electric current and the above-mentioned cause. Accordingly, the exposure amount of the electron beam, i.e., an exposure time must be increased to reliably perform the drawing so that there is a subject of badness in efficiency.

[0005] On the other hand, an emission source constructed by arranging many carbon nanotubes in a plane substrate is recently vigorously considered as a new emission source for a display device. This is because the carbon nanotube has the following characteristics. Namely, since the tip diameter of the carbon nanotube is very small at a nano level, the field emission can be performed even at low voltage. Further, since the bonding between carbon atoms is very strong in comparison with a metal, the carbon nanotube is strong against the above ion impact, and the emission electric current is excellent in stability and an electron is emitted even in a relatively low vacuum.

[0006] Therefore, if a single carbon nanotube, or a bundle-shaped carbon nanotube having several carbon nanotubes apparently set to one bundle is applied to the emission source of the electron microscope and the electron beam drawing device, an electron emission site is at a nano level so that an electron emission angle is small and the energy width of the emitted electron is small. Therefore, high resolution and high definition processing can be performed in comparison with the conventional case.

[0007] However, there is almost no consideration example in which the single carbon nanotube, or the bundle-shaped carbon nanotube having plural carbon nanotubes apparently set to one bundle is applied to the emission source of the electron microscope and the electron beam drawing device. With respect to the field emission characteristics of the single carbon nanotube, for example, there are only a report of M. J. Fransen, Th. L. van Rooy, P. Kruit, Appl. Surface Sci. 146(1999) 312-327, etc.

[0008] The carbon nanotube emission source used in the above report has a structure fixed by carbon contamination on the tip side face of a tungsten needle as a base material as shown in FIG. 1. In such a structure, since the contact area of the tungsten needle and the carbon nanotube is very reduced, the following problems cannot be solved when this structure is applied to the emission source of the electron microscope and the electron beam drawing device. (1) No ohmic contact of the carbon nanotube and the tungsten needle is made, and electric resistance in a joining portion is increased, and electric field intensity at the carbon nanotube tip is considerably reduced in comparison with the applied voltage so that a field emission threshold voltage is increased. (2) In a state in which an electric current flows to a certain extent, the supply of an electron to an electron emission site is prevented for the above reasons, and the electric current is saturated even when a greater voltage is applied. Accordingly, no large electric current can be obtained. (3) Heat generating amount in the joining portion is increased for the above reasons so that the tungsten needle as a base material is dissolved. (4) Since joining strength is small, the joining portion is easily separated by charging of static electricity, impact, etc. (5) Since the carbon nanotube is attached to the side face of the tungsten needle, it becomes difficult to adjust an electron beam axis after assembly into an electron gun.

[0009] A method for coating the tip portion of an electrically conductive needle with catalyst metallic particles and directly growing the carbon nanotube from the catalyst metallic particles by the CVD method, etc. is known. However, there is no example of manufacture of the carbon nanotube excellent in electron emission characteristics simultaneously satisfying crystallinity, purity and fineness property, of the grown carbon nanotube. Further, the diameter of the grown carbon nanotube depends on the diameter of the catalyst metallic particle, and it is necessary to arrange one catalyst metallic nano-particle at the electrically conductive needle tip so that it is considerably difficult in manufacture. Even when one carbon nanotube can be grown from the catalyst metallic nano-particle, the catalyst metallic particle is moved in a carbon nanotube growing direction together with the growth of the carbon nanotube. Therefore, the catalyst metallic particle is lost in the joining portion of the electrically conductive needle and the carbon nanotube so that no problems caused by the above joining defect can be solved. Further, when the catalyst metallic particle is left, a subject also exists in that plural carbon nanotubes are grown at random from this catalyst metallic particle.

SUMMARY OF THE INVENTION

[0010] Accordingly, an object of the present invention is to provide a high reliability emission source able to sufficiently secure the ohmic contact of the carbon nanotube and an electrically conductive base material, and having sufficient joining strength and easily making a beam shaft adjustment.

[0011] One of means for achieving the above object resides in an emission source having a carbon nanotube and characterized in that the emission source has an electrically conductive base material and a carbon nanotube coming in ohmic contact with the electrically conductive base material.

[0012] Otherwise, the carbon nanotube coming in ohmic contact with the electrically conductive base material is characterized in that this carbon nanotube has an electrically conductive joining material joined to said electrically conductive base material, and a carbon nanotube joined to the electrically conductive joining material. Thus, electric resistance in a joining portion can be reduced, and an increase in field emission threshold voltage can be prevented, and the supply amount of electrons to an electron emission site is increased. Further, the generating amount of heat in the joining portion is restrained, and melting, etc. of the electrically conductive base material are prevented, and reliability as the emission source can be raised.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a view showing a conventional joining method of a carbon nanotube and an electrically conductive base material.

[0014]FIG. 2 is a view showing an emission source in accordance with an embodiment 1.

[0015]FIG. 3 is a view showing another example of the emission source in accordance with the embodiment 1.

[0016]FIG. 4 is a view showing an emission source in accordance with an embodiment 2.

[0017]FIG. 5 is a view showing an emission source in accordance with an embodiment 3.

[0018]FIG. 6A is a view showing an emission source in accordance with an embodiment 4, and FIG. 6B is a view showing the emission source in accordance with the embodiment 4.

[0019]FIG. 7 is a view showing an emission source in accordance with an embodiment 5.

[0020]FIG. 8A is a view showing an emission source in accordance with an embodiment 6, and FIG. 8B is a view showing the emission source in accordance with the embodiment 6.

[0021]FIG. 9 is a view showing an emission source in accordance with an embodiment 7.

[0022]FIG. 10A is a view showing an electron microscope in accordance with an embodiment 8, and FIG. 10B is a view showing the electron microscope in accordance with the embodiment 8.

[0023]FIG. 11 is a view showing an electron beam drawing device in accordance with the embodiment 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The embodiment modes of the present invention will be explained in detail with reference to the drawings. An electrically conductive needle and an electrically conductive plate in this specification are set to one example of an electrically conductive base material.

[0025] (Embodiment 1)

[0026]FIG. 2 shows an emission source in accordance with this embodiment. The emission source in accordance with this embodiment is constructed such that the emission source has an electrically conductive needle having a micro hole at its tip, an electrically conductive joining material having a melting point lower than that of the electrically conductive needle and arranged in the micro hole, and a carbon nanotube attached to the electrically conductive joining material. Thus, the problem with respect to the joining property of the carbon nanotube and the electrically conductive needle in the emission source can be solved, and the carbon nanotube and the electrically conductive needle can stably come in ohmic contact with each other.

[0027] A metal or carbon excellent in electrically conductive property, thermal conductive property and oxidation resisting property and having a relatively high melting point is preferable as the material of the electrically conductive needle for attaching the carbon nanotube. Tungsten, molybdenum, titanium, platinum, gold or an alloy having these elements is used as the metal, but the metal is not limited to these materials.

[0028] The electrically conductive joining material for coating the electrically conductive needle is not particularly limited if wettability with the carbon nanotube and the electrically conductive base material is relatively good, and the coefficient of thermal expansion of the electrically conductive joining material is preferably close to that of the electrically conductive base material, and the electrically conductive joining material is melted at a temperature equal to or lower than the melting point of the electrically conductive base material, and is melted at a temperature or less not decomposed even when the carbon nanotube is heated in a vacuum. In view of manufacture property, a metal having a melting point of 1500° C. or less is desirable, and a metal or an alloy constructed by at least one of lithium, beryllium, magnesium, aluminum, potassium, calcium, manganese, cobalt, nickel, rubidium, strontium, tellurium, cesium, barium, lanthanum, bismuth, lead, tin, indium, cadmium, copper, sulfur, selenium, gallium, etc. is used.

[0029] The emission source in accordance with this embodiment may be constructed such that the tip portion of the electrically conductive needle forming no micro hole therein is coated with the electrically conductive joining material having a melting point lower than that of the electrically conductive needle, and the carbon nanotube is attached to the tip portion. However, as shown in FIG. 2, it is more desirable in view of joining reliability to arrange the micro hole in the tip center portion of the electrically conductive needle. Further, as shown in FIG. 3, the micro hole is not arranged in the tip center portion of the electrically conductive needle, but a concave portion may be formed in one portion of the electrically conductive needle, and the electrically conductive joining material may be arranged in this concave portion, and the carbon nanotube may be attached to the concave portion.

[0030] A manufacturing method of the emission source in accordance with this embodiment will next be shown. First, a micro hole (or a concave portion, etc.) is formed by FIB processing or the photolithograph method, etc. in the tip center portion of the electrically conductive needle sharpened at its tip by etching, etc. Thereafter, the tip portion of the electrically conductive needle is coated with the electrically conductive joining material having a melting point lower than that of the electrically conductive needle by sputtering, evaporation, or dipping, etc. This becomes a material for attaching the carbon nanotube. One carbon nanotube is then inserted into the micro hole coated with the electrically conductive joining material, and the base material is cooled and solidified until a solidifying temperature of the electrically conductive joining material. Thus, the emission source shown in FIG. 2 can be manufactured.

[0031] Thus, the ohmic contact of the carbon nanotube and the electrically conductive base material can be secured, and the emission source of high reliability having sufficient joining strength can be provided. Further, it is possible to reduce sample damage due to formation for high resolution, high brightness and a low acceleration voltage in comparison with the conventional device kind by using this emission source in an electron microscope. Further, since an electron emission angle is small, the diaphragm degree of an electron beam using a condenser lens is reduced so that one portion or all of the condenser lens can be omitted. Further, in comparison with the conventional emission source, an electron is emitted even in a low vacuum degree so that a vacuum exhaust system can be simplified. Further, in comparison with the conventional device kind, the acceleration voltage can be reduced so that heat generation around an electron gun is reduced and an electron gun circumference can be sufficiently cooled by the air without cooling the electron gun circumference by cooling water as in the conventional device kind. Accordingly, since a cooling system can be omitted or simplified, it is possible to provide an electron microscope for realizing a reduction in cost and compactness, and an electron beam drawing device for realizing high definition, high efficiency, a reduction in cost and compactness. The electrically conductive needle used for the explanation in this embodiment is one example of the electrically conductive base material, and is explained as a mode able to emit the electron most efficiently.

[0032] (Embodiment 2)

[0033]FIG. 4 shows an emission source in accordance with this embodiment. The emission source in accordance with this embodiment is constructed such that the carbon nanotube of the emission source described in the embodiment 1 is coated with several layers of an electrically conductive material having a melting point higher than that of the electrically conductive joining material (coating layers are arranged). In accordance with this construction, even when the wettability of the electrically conductive joining material with the carbon nanotube is not so good, the wettability can be improved as a whole and joining reliability can be raised by nipping a material having good wettability with both the electrically conductive joining material and the carbon nanotube. Further, ion resisting impact property can be further improved by arranging a coating layer around the carbon nanotube. In this case, when the layer (coating layer) for coating the carbon nanotube is too thick, the advantage of a small diameter with respect to the carbon nanotube is reduced. Therefore, each coating layer is preferably set to have a thickness of about several nm to several ten nm.

[0034] Here, a concrete example with respect to the emission source in accordance with this embodiment will be explained by using FIG. 4. The electrically conductive needle is formed by tungsten, and the electrically conductive joining material is formed by a tin-based low melting point alloy. Since wettability is not so good with respect to the tin-based low melting point metal alloy and the carbon nanotube, a metal having good wettability with the carbon nanotube, e.g., titanium, hafnium, zirconium, tantalum, niobium, chromium, molybdenum, manganese, aluminum, calcium, iron, nickel, cobalt, tungsten, silicon, etc. easy to form a carbide are first formed as a first metal coating layer. Copper, nickel, silver, gold, etc. as a metal having good wettability with both the first metal coating layer and the tin-based low melting point alloy and a melting point higher than that of the tin-based low melting point alloy are formed as a second metal coating layer outside the first metal coating layer. Thus, the wettability with the electrically conductive joining material can be gradually raised from the carbon nanotube side, and the tolerance of a material selection can be raised and ion resisting impact property can be improved.

[0035] Since wettability is also not so good with respect to tungsten and the tin-based low melting point alloy as the electrically conductive needle, a metal such as copper, nickel, silver, gold, etc. having good wettability with both tungsten and the tin-based low melting point alloy and a melting point higher than that of the tin-based low melting point alloy is preferably formed as a metal coating layer in the entire electrically conductive needle or the tip portion (the micro hole interior or the concave portion). It is free whether or not the metal coating layer is arranged in accordance with the wettability. Further, it is possible to select that the metal coating layer is arranged in the entire carbon nanotube, or is arranged only in a portion relating to the joining in accordance with necessity. In this meaning, the coating with the metal coating layer is not only the entire coating case, but also includes that the metal coating layer is arranged only in the portion relating to the joining.

[0036] Further, no carbon nanotube is particularly limited, but one carbon nanotube is preferable in view of the size of the emission source. However, when a large electric current is required as in an electron beam drawing device, etc., a bundle-shaped carbon nanotube of several carbon nanotubes (including the metal coating layers) apparently seen as one bundle may be also used if the entire diameter is 100 nm or less.

[0037] There are the evaporation method, the CVD method, the sputtering method, etc. as the manufacturing method of these metal coating layers.

[0038] As mentioned above, it is possible to provide the emission source of high reliability able to secure ohmic contact with the carbon nanotube and the electrically conductive base material, and having sufficient joining strength and good wettability between the respective materials and a high ion resisting impact property. Further, it is possible to provide an electron microscope for realizing high resolution, high brightness, a reduction in sample damage due to a reduction in acceleration voltage, a reduction in cost and compactness, and an electron beam drawing device for realizing high definition, high efficiency, a reduction in cost and compactness in comparison with the conventional device kind by using this emission source in the electron microscope.

[0039] (Embodiment 3)

[0040]FIG. 5 shows an emission source in accordance with this embodiment.

[0041] The emission source in FIG. 5 is constructed such that this emission source has an electrically conductive plate having a sharp tip shape (tip portion) and a micro hole in its tip portion, an electrically conductive joining material having a melting point lower than that of the electrically conductive needle arranged in the micro hole, and a carbon nanotube attached to the electrically conductive joining material. With respect to the shape of the electrically conductive base material for attaching the carbon nanotube, the tip of the electrically conductive plate is preferably sharp to a certain extent since an electric field is easily concentrated onto the tip as the tip shape is sharpened.

[0042] (Embodiment 4)

[0043]FIGS. 6A and 6B show emission sources in accordance with this embodiment.

[0044] The emission source in FIG. 6A is constructed such that this emission source has an electrically conductive base material of a V-shaped filament shape having a micro hole in a V-shaped portion (tip portion), an electrically conductive joining material having a melting point lower than that of an electrically conductive needle arranged in the micro hole, and a carbon nanotube attached to the electrically conductive joining material.

[0045] The emission source in FIG. 6B is constructed such that this emission source has an electrically conductive base material having a V-shaped filament shape, an electrically conductive needle attached to the V-shaped portion (tip portion) of the electrically conductive base material having the V-shaped filament shape and having a micro hole at the tip, an electrically conductive joining material having a melting point lower than that of the electrically conductive needle arranged in the micro hole, and a carbon nanotube attached to the electrically conductive joining material.

[0046] With respect to the shape of the electrically conductive base material for attaching the carbon nanotube, the electric field is easily concentrated onto the tip as the tip shape is sharpened. Therefore, it is possible to realize the emission source of high output and high reliability by concentrating the electric field by forming the sharp plate to a certain extent. Further, since the electrically conductive base material is formed in the V-shaped filament shape in the emission source in accordance with this embodiment, the attached carbon nanotube can be easily heated by flowing an electric current through the filament, and an adsorbing gas on the carbon nanotube surface can be removed.

[0047] As mentioned above, it is possible to provide the emission source of high reliability able to secure the ohmic contact of the carbon nanotube and the electrically conductive base material and having sufficient joining strength and able to remove the adsorbing gas on the carbon nanotube surface.

[0048] (Embodiment 5)

[0049] An emission source in accordance with this embodiment will be explained by using FIG. 7. The emission source in accordance with this embodiment is constructed such that the circumference of a joining portion of the carbon nanotube and the electrically conductive joining material in the emission source manufactured in the embodiment 1 is coated with a high melting point metal or carbon, and a coating material for sealing the electrically conductive joining material is arranged. In other words, this embodiment is characterized in that the emission source has the coating material and the electrically conductive joining material is sealed by the coating material and the electrically conductive base material.

[0050] The joining state can be secured by arranging the coating material in this way even when the emission source becomes a temperature equal to or greater than the melting point of the electrically conductive joining material. The high melting point metal in this case means a metal having a melting point higher than that of the electrically conductive joining material, and this melting point is desirably set to 1500° C. or more. Further, in this case, the electrically conductive joining material can be omitted, but it is more preferable to use the electrically conductive joining material in view of manufacture.

[0051] This emission source can be manufactured by locally evaporating tungsten, carbon, etc. only near the joining portion while irradiation damage of the carbon nanotube itself during the observation of an image is minimized by an FIB processor, etc. utilizing an electron beam instead of e.g., gallium ions near the joining portion of the emission source manufactured by the method described in the embodiment 1.

[0052] In this embodiment, the emission source is manufactured with the emission source manufactured in the embodiment 1 as a source. However, it is not limited to the emission source manufactured by the embodiment 1, but the emission source can be also manufactured with respect to the emission source described in one of the embodiments 1 to 4 as long as the above effects are obtained.

[0053] As mentioned above, it is possible to provide the emission source of high reliability able to secure the ohmic contact of the carbon nanotube and the electrically conductive base material, and having sufficient joining strength and able to secure the joining state even when the emission source is exposed to a temperature equal to or greater than the melting point of a low melting point metal.

[0054] (Embodiment 6)

[0055] In this embodiment, an operating method of the emission source using the emission source disclosed in each of the embodiments 4 and 5 will be explained by using FIGS. 8A and 8B.

[0056] Namely, the emission source in FIG. 8A is constructed such that this emission source has an electrically conductive base material of a V-shaped filament shape having a micro hole in a V-shaped portion (tip portion), an electrically conductive joining material having a melting point lower than that of an electrically conductive needle arranged in the micro hole, a carbon nanotube attached to the electrically conductive joining material, and a coating material arranged to seal the above electrically conductive joining material near the joining portion of the carbon nanotube and the above electrically conductive joining material. The emission source in FIG. 8B is constructed such that this emission source has an electrically conductive base material having a V-shaped filament shape, an electrically conductive needle attached to the V-shaped portion (tip portion) of the electrically conductive base material having the V-shaped filament shape and having a micro hole at the tip, an electrically conductive joining material having a melting point lower than that of the electrically conductive needle arranged in the micro hole, a carbon nanotube attached to the electrically conductive joining material, and a coating material arranged to seal the above electrically conductive joining material near the joining portion of the carbon nanotube and the above electrically conductive joining material. A flashing free operating method can be executed by using this emission source. This operating method will next be explained concretely.

[0057] In the emission source having this construction, the joining state can be secured even when the emission source is exposed to a temperature equal to or greater than the melting point of the electrically conductive joining material having a low melting point. Therefore, for example, when a critical temperature causing thermal field electron emission from the carbon nanotube is set to T₁, and a temperature for separating an adsorbing gas on the carbon nanotube surface is set to T₂, and the heating temperature of the carbon nanotube is set to T, the electron beam of a narrow energy width can be stably obtained over a long period without performing conventionally indispensable flashing even in a vacuum degree considerably lower than the vacuum degree required in the conventional field emission source by operating the emission source as T₂<T<T₁ by adjusting an electric current amount to a filament. Here, the above T₂ ranges from 500 to 1000° C. However, if the used carbon nanotube lies in a temperature range not decomposed by heating, the above T₂ may also lie in a temperature range equal to or greater than this temperature range. In particular, in a length measuring SEM (CDSEM) used in relation to a semiconductor at present, it is indispensable that it is flashing free. Therefore, only a Schottky type emission source inferior in resolution in comparison with the field emission type is used. However, a flashing free high resolution observation can be made by executing the emission source in accordance with this embodiment by the above operating method.

[0058] (Embodiment 7)

[0059] Another example with respect to the manufacturing method of the emission source described in the embodiment 1 is shown in this embodiment. This embodiment differs from the embodiment 1 in that the electrically conductive joining material is an organic material changed to graphite.

[0060] The manufacturing method of the emission source in accordance with this embodiment is a method for making the emission source described in e.g., the embodiment 1. In this method, a micro hole is formed by FIB processing or the photolithograph method, etc. in the tip center portion of an electrically conductive needle sharpened at the tip by etching, etc. The electrically conductive needle having the micro hole in the electrically conductive tip portion is coated with an organic material in advance, and one carbon nanotube is inserted into the micro hole coated with the organic material and is temporarily fixed. This carbon nanotube is heated until a temperature for carbonizing the organic material within a vacuum or an inactive gas atmosphere so that the organic material is changed to graphite. Namely, the organic material is changed to graphite having an electrically conductive property by this process. Therefore, it is possible to manufacture an emission source in which the carbon nanotube and the electrically conductive needle are joined to each other in ohmic contact. If the electrically conductive needle is particularly constructed by carbon in this case, all the materials constituting the emission source are constructed by carbon. Therefore, it is very advantageous since the problem with respect to different kind material joining such as interface separation in the joining portion caused by a difference in thermal expansion, wettability between the respective materials, etc. can be solved.

[0061] In this embodiment, the explanation is made with the emission source described in the embodiment 1 as a source. However, this embodiment can be also applied to the manufacturing method of the emission source in accordance with the embodiments 2 to 6 as long as the above manufacture process can be performed (in this case, it is possible to cope with the application by suitably reading a concave portion for the micro hole, etc.).

[0062] Further, after the carbon nanotube is temporarily fixed by carbon contamination, etc. to an electrically conductive base material having the concave portion formed in the tip center portion as shown in FIG. 3 as an embodiment mode or an electrically conductive base material having a tip sectional portion flattened as shown in FIG. 9, the carbon nanotube and the electrically conductive base material can be diffusively joined to each other by heating the carbon nanotube within a vacuum or an inactive gas. A metal easy to form the carbon nanotube and an intermediate product such as an electrically conductive carbide, etc. is preferable as the electrically conductive base material. For example, Ti, W, etc. are used as the electrically conductive base material. The heating temperature in this case preferably ranges from 500 to 1000° C. If a particle beam such as ions, an electron beam, etc. is simultaneously irradiated to only the joining portion, the diffusion between the carbon nanotube and the electrically conductive base material is accelerated so that the diffusive joining can be performed for a short time at a lower temperature.

[0063] (Embodiment 8)

[0064] This embodiment is an example in which the emission source in accordance with the embodiment 1 is used in an electron gun. FIG. 10A shows its construction. FIG. 10B shows an example in which this electron gun is further used in a scanning type microscope.

[0065] The electron gun shown in FIG. 10A is constructed such that this electron gun has an emission source, a strut for supporting the emission source, an insulating substrate for fixing the strut, a first anode and a second anode.

[0066] The scanning type microscope shown in FIG. 10B is constructed by an electron optical system for reducing the size of an electron beam emitted from an electron gun by an electron lens and focusing and forming a micro electron probe on a sample face, and moving and scanning the electron probe on the sample by a deflecting device, a sample chamber, and an exhaust system for maintaining the electron optical system and the sample chamber in a vacuum. The construction of an electron optical system in a length measuring SEM (CDSEM) for observing a micro processing pattern in a semiconductor process and measuring the size of this pattern, and an electron beam drawing device for forming various kinds of circuit patterns by irradiating the electron beam to a sample substrate coated with a resist sensitive to the electron beam is also basically the same as FIG. 10.

[0067] As mentioned above, it is possible to provide an electron microscope for realizing high resolution, high brightness, a reduction in sample damage due to a reduction in acceleration voltage, a reduction in cost and compactness, and an electron microscope and an electron beam drawing device for realizing high definition, high efficiency, a reduction in cost and compactness in comparison with the conventional device kind by applying the field emission source in accordance with the embodiment 1 to the electron gun of these devices.

[0068] Further, with respect to the electron beam drawing device, a multi-electron beam source mounting type electron beam drawing device manufactured by two-dimensionally arranging a thin film type emission source (MIM) constructed by a three-layer structure of metal-insulator-metal in a grid shape is recently devised. Patterns can be collectively transferred by this drawing device so that throughput can be greatly improved in comparison with one emission source. However, in this case, the electron emission threshold field of the MIM is very high as in 1 to 10 MV/cm or more. Therefore, a problem exists in that dielectric breakdown of the insulator or a driving circuit part constituting the MIM, etc. are caused. Accordingly, an emission source able to achieve high electric current density at low voltage is required. Therefore, the above problem can be solved by mounting the emission source of the present invention as shown in FIG. 10.

[0069] Similar to the scanning type electron microscope, the fundamental principle of the electronic optical system is the same in a scanning transmission electron microscope in which the electron beam emitted from the emission source is thinly diaphragmed by plural electron lenses, and an image is obtained by scanning this electron beam in a rectangular shape by using a scanning coil, and a transmission type electron microscope

BACKGROUND OF THE INVENTION

[0070] The present invention relates to an emission source having a carbon nanotube, and to an electron microscope and an electron beam drawing device using this emission source.

[0071] The following four conditions are required to further increase the resolution and brightness of an electron microscope. (1) The size of the emission source needs to be reduced. (2) The brightness of the emission source needs to be increased. (3) The electron energy width from the emission source needs to be reduced so as to reduce the influence of chromatic aberration. (4) The emitted electron beam needs to be stabilized.

[0072] There are various known types of electron emission source, including a thermal type made of LaB₆, a Schottky type made of ZrO/W, and a field emission type made of tungsten in which the tip of a needle is sharpened by electric field polishing. From the point of view of high resolution and high brightness, the emission source of the field emission type is excellent, but it has the following defects. (1) Since no field emission is generated unless a super high vacuum state of 10⁻⁸ Pa or more is set, an exhaust system of large-size is required, so that it is difficult to make the device compact, and the cost is increased. (2) Since no field emission is generated unless the drawing-out voltage is set to a high value, such as several kV, an organic material and an organism relating sample, which hold promise for rapid 

What is claimed is:
 1. An emission source comprising: an electrically conductive needle having a micro hole; an electrically conductive joining material arranged in the micro hole of the electrically conductive needle; and a carbon nanotube joined to said electrically conductive joining material.
 2. The emission source according to claim 1, wherein said electrically conductive joining material is a metal having a melting point lower than that of said electrically conductive needle.
 3. The emission source according to claim 1, wherein said carbon nanotube is coated with a first metallic coating layer having a melting point higher than that of said electrically conductive joining material.
 4. The emission source according to claim 3, wherein said carbon nanotube has a second metallic coating layer having a melting point higher than that of said electrically conductive joining material, and coating said first metallic coating layer.
 5. The emission source according to claim 1, wherein the emission source further comprises a coating material, and said electrically conductive joining material is sealed by the coating material and said electrically conductive needle.
 6. The emission source according to claim 1, wherein a metallic coating layer having a melting point higher than that of said electrically conductive joining material is arranged between said electrically conductive needle and the electrically conductive joining material.
 7. The emission source according to claim 1, wherein said electrically conductive joining material is constructed by carbonization-processing an organic material.
 8. The emission source according to claim 1, wherein said electrically conductive needle is arranged in an electrically conductive base material of a V-shaped filament shape.
 9. An emission source comprising an electrically conductive base material and a carbon nanotube coming in ohmic contact with the electrically conductive base material.
 10. The emission source according to claim 9, wherein the carbon nanotube coming in ohmic contact with the electrically conductive base material has: an electrically conductive joining material joined to said electrically conductive base material, and a carbon nanotube joined to the electrically conductive joining material.
 11. The emission source according to claim 10, wherein said electrically conductive joining material is a metal having a melting point lower than that of said electrically conductive base material.
 12. The emission source according to claim 10, wherein said carbon nanotube is coated with a first metallic coating layer having a melting point higher than that of said electrically conductive joining material.
 13. The emission source according to claim 10, wherein said electrically conductive base material is formed in a V-shaped filament shape.
 14. The emission source according to claim 10, wherein said electrically conductive joining material is constructed by carbonization-processing an organic material.
 15. A manufacturing method of an emission source comprising a process for making an electrically conductive base material and a carbon nanotube come in ohmic contact with each other.
 16. The manufacturing method of the emission source according to claim 15, wherein the process for making said electrically conductive base material and the carbon nanotube come in ohmic contact with each other is constructed by: a process for arranging an electrically conductive joining material in the electrically conductive base material; and a process for inserting the carbon nanotube into the electrically conductive joining material.
 17. The manufacturing method of the emission source according to claim 16, wherein the process for inserting the carbon nanotube into said electrically conductive joining material is a process for melting a metal as said electrically conductive joining material, inserting the carbon nanotube into the melted electrically conductive joining material, and cooling and solidifying the metal as said electrically conductive joining material.
 18. The manufacturing method of the emission source according to claim 15, wherein the process for making said electrically conductive base material and the carbon nanotube come in ohmic contact with each other is a process for diffusively joining said electrically conductive base material and said carbon nanotube by taking heat treatment after the carbon nanotube is fixed to the electrically conductive base material by carbon contamination.
 19. An electron microscope characterized in that the emission source according to claim 1 is used.
 20. An electron beam drawing device characterized in that the emission source according to claim 1 is used.
 1. (original) An emission source comprising: an electrically conductive needle having a micro hole; an electrically conductive joining material arranged in the micro hole of the electrically conductive needle; and a carbon nanotube joined to said electrically conductive joining material.
 2. (original) The emission source according to claim 1, wherein said electrically conductive joining material is a metal having a melting point lower than that of said electrically conductive needle.
 3. (original) The emission source according to claim 1, wherein said carbon nanotube is coated with a first metallic coating layer having a melting point higher than that of said electrically conductive joining material.
 4. (original) The emission source according to claim 3, wherein said carbon nanotube has a second metallic coating layer having a melting point higher than that of said electrically conductive joining material, and coating said first metallic coating layer.
 5. (original) The emission source according to claim 1, wherein the emission source further comprises a coating material, and said electrically conductive joining material is sealed by the coating material and said electrically conductive needle.
 6. (original) The emission source according to claim 1, wherein a metallic coating layer having a melting point higher than that of said electrically conductive joining material is arranged between said electrically conductive needle and the electrically conductive joining material.
 7. (original) The emission source according to claim 1, wherein said electrically conductive joining material is constructed by carbonization-processing an organic material.
 8. (original) The emission source according to claim 1, wherein said electrically conductive needle is arranged in an electrically conductive base material of a V-shaped filament shape.
 9. (original) An emission source comprising an electrically conductive base material and a carbon nanotube coming in ohmic contact with the electrically conductive base material.
 10. (original) The emission source according to claim 9, wherein the carbon nanotube coming in ohmic contact with the electrically conductive base material has: an electrically conductive joining material joined to said electrically conductive base material, and a carbon nanotube joined to the electrically conductive joining material.
 11. (original) The emission source according to claim 10, wherein said electrically conductive joining material is a metal having a melting point lower than that of said electrically conductive base material.
 12. (original) The emission source according to claim 10, wherein said carbon nanotube is coated with a first metallic coating layer having a melting point higher than that of said electrically conductive joining material.
 13. (original) The emission source according to claim 10, wherein said electrically conductive base material is formed in a V-shaped filament shape.
 14. (original) The emission source according to claim 10, wherein said electrically conductive joining material is constructed by carbonization-processing an organic material.
 15. (original) A manufacturing method of an emission source comprising a process for making an electrically conductive base material and a carbon nanotube come in ohmic contact with each other.
 16. (original) The manufacturing method of the emission source according to claim 15, wherein the process for making said electrically conductive base material and the carbon nanotube come in ohmic contact with each other is constructed by: a process for arranging an electrically conductive joining material in the electrically conductive base material; and a process for inserting the carbon nanotube into the electrically conductive joining material.
 17. (original) The manufacturing method of the emission source according to claim 16, wherein the process for inserting the carbon nanotube into said electrically conductive joining material is a process for melting a metal as said electrically conductive joining material, inserting the carbon nanotube into the melted electrically conductive joining material, and cooling and solidifying the metal as said electrically conductive joining material.
 18. (original) The manufacturing method of the emission source according to claim 15, wherein the process for making said electrically conductive base material and the carbon nanotube come in ohmic contact with each other is a process for diffusively joining said electrically conductive base material and said carbon nanotube by taking heat treatment after the carbon nanotube is fixed to the electrically conductive base material by carbon contamination.
 19. (original) An electron microscope characterized in that the emission source according to claim 1 is used.
 20. (original) An electron beam drawing device characterized in that the emission source according to claim 1 is used. 